The present invention relates to a method for forming a photoresist, and more particularly relates to a method for forming a cross-linking chemically amplified resist in a semiconductor manufacturing process.
As the integration of the semiconductor device is increasing, the scale of the semiconductor device is getting smaller. To successfully manufacturing a semiconductor device, a photolithography process is more important than ever. An example of a photolithography process is shown in FIG. 1. A deep ultra violet (DUV) ray 4 having a wavelength of 248 nano-meter (nm) is illuminated from a light source (not shown) to a mask 3. The pattern formed on the mask 3 will be transferred to the positive photoresist layer 2 coated on the surface of the substrate 1 through the illumination of the DUV ray 4. After a post exposure bake step, the pattern transferred to the photoresist layer 2 is formed by a development procedure.
As the line width of the pattern on the mask become smaller, a more exact photolithography process is needed. Methods for increasing the resolution of the transferred pattern are developed. Some of them are the utilization of phase shifting mask, the technique of the off-axis illumination, the utilization of an anti-reflection layer, and the utilization of a thinner resist layer, etc.
Among the above-mentioned method, using a thinner resist layer is not even convenient but also effective. The thinner the photoresist is, the higher the resolution of the transferred pattern is obtained. That is because a thinner photoresist can bear a higher vibration and/or miss-alignment than a thick photoresist. Accordingly, the thinner photoresist layer will have a uniform focus from the top surface to the bottom portion.
However, a photoresist layer cannot be too thin. When the thickness of a photoresist layer is reduced to a certain value, the etch-resistance of the photoresist layer will be influenced. Accordingly, the structure on the substrate will be damaged during the succeeding etching or ion-implanting process. In other words, the reduction of the photoresist layer thickness is limited at the etch-resistance of the photoresist layer.
To make the photoresist layer further thinner, the etch-resistance and/or the ion-implant-resistance of the photoresist must be enhanced. Usually, a hard bake process is used to increase the etch-resistance by reducing the amount of the solvent remained in the photoresist layer and increasing the adhesion between the photoresist layer and the substrate. However, the hard bake process only provides a very little improvement to the etch-resistance of the photoresist layer. The hard bake process does not cause any chemical reaction. The intrinsic property of the photoresist layer cannot be changed by the hard bake process.
It is then attempted by the Applicant to solve the above-mentioned problems.
An object of the present invention is to provide a relatively thin photoresist layer which has a good etch-resistance and ion-implant-resistance.
According to the present invention, a method for forming a cross-linking photoresist layer is provided. The method includes steps of providing a photoresist layer; activating the photoresist layer with a light provided by a light source; and putting the photoresist layer in a vapor of a cross-linking agent to form the cross-linking photoresist layer.
The photoresist layer is preferably a patterned photoresist layer. More preferably, the photoresist layer is a chemically amplified resist layer.
The activating light is preferably an ultra violet (UV) ray having a wave length of about 365 nm
Of course, the method may further include a step of baking the photoresist layer after the photoresist layer is activated by the light.
The cross-linking agent is preferably butadiene diepoxy (BTDE).
The cross-linking photoresist layer is preferably formed at a temperature ranged between about 80xc2x0 C. to about 120xc2x0 C. Preferably, the temperature is about 100xc2x0 C. The temperature is obtained by heating the photoresist layer by a hot plate. The photoresist layer is preferably heated for about 10 seconds to 30 minutes.
Preferably, the photoresist layer is provided on a substrate.
The present invention further provides a semiconductor structure. The semiconductor includes a substrate; a patterned photoresist layer formed on the substrate; and a cross-linking structure covering the surface of the patterned photoresist layer.
Preferably, the patterned photoresist layer is a chemically amplified resist layer. The patterned photoresist layer preferably has a structure of: 
Preferably, the cross-linking structure has a structure of: 
According to another aspect of the present invention, a method for manufacturing a semiconductor device is provided. The method includes steps of forming a photoresist layer on a substrate; patterning the photoresist layer; forming a cross-linking layer over the surface of the photoresist layer; and etching the semiconductor structure with a mask composed of the photoresist layer and the cross-linking layer.
The photoresist layer is preferably a chemically amplified resist layer. The photoresist layer preferably has a structure of: 
Steps for forming the cross-linking layer preferably include activating the photoresist layer to generate thereon a hydroxy group; and putting the photoresist layer into an atmosphere of a cross-linking agent to generate the cross-linking layer.
Preferably, the photoresist layer is heated by a hot plate at a temperature of about 100xc2x0 C. when being put into the atmosphere of the cross-linking agent. The cross-linking agent is preferably butadiene diepoxy, and the photoresist layer is preferably heated by the hot plate for about 10 seconds to 30 minutes.
The photoresist layer is preferably activated by ultra violet ray having a wavelength of about 365 nm.
The method may further includes a step of implanting the semiconductor structure with the mask.